Tissue engineering is developing toward clinical applications for the repair and restoration of damaged or diseased tissues and organs. In particular, the development of vascular grafts is a major goal in the field of vascular surgery. Cardiovascular disease is the leading cause of mortality and morbidity in the first world. The standard of care, the autograft, is not without serious morbidity. Patients with systemic disease, leaving no appropriate autograft material or having already undergone autografts, number 100,000 a year in the United States alone and have few autograft options.
Vessels have mechanical and biological failure modes caused by thrombosis within the vessel and subsequent occlusion and/or cellular ingrowth. Synthetic vessels having material properties capable of withstanding arterial pressure are commonplace, making the search for non-thrombogenic materials a prime research interest. Endothelial cells obtained from the patient have been shown to decrease the thrombogenicity of implanted vessels (Williams et al., 1994, J. Vasc. Surg., 19:594-604; Arts et al., 2001 Lab Invest 81:1461-1465), but to date placement of the cells upon the graft have been lengthy processes not suited to the operating room.
Pressure gradients involving transient (from a few seconds to less than one minute) relatively high pressures (5 PSI or 259 mm Hg) have previously been used to deposit cells onto a porous graft scaffold. The cells are deposited by a sieving action provided by bulk flow of a cellular suspension against a substrate or scaffold material having pores smaller than the cell population, thus capturing cells in the matrix (e.g., U.S. Pat. No. 5,628,781; Williams et al., 1994, J. Vasc. Surg., 1Q: 594-004; Williams et al., 1992, J Biomed Mat Res 26:103-117; Williams et al., 1992, J. Biomed Mat Res 28:203-212). The captured cells have been shown to subsequently adhere to the scaffold material to improve the patency of peripheral grafts. However, clinical applicability in the coronary position has been limited to date, at least in part because the resulting vessels do not maintain sufficiently cohesive non-thrombogenic surfaces. In response, research has focused on additional cell maturation time in vitro.
What is needed are methods and apparatus to achieve rapid cellular adhesion in or on permeable substrate materials in a matter of minutes or hours, with instruments that lend themselves to the operating room environment, maintain a sterile barrier, are easy to use, produce consistent graft results and are relatively inexpensive.